The present invention relates to a nonflammable wave absorbing material, a method of manufacturing the same, and a nonflammable construction material having wave absorbing properties and, more particularly, to a wave absorbing material that holds non-flammability or semi-nonflammability and flexibility to cancel the brittleness and has advantageous properties regarding the lightness in weight, the thermal insulation, the sound insulation, the sound isolation, and the workability.
Wave anechoic rooms and semi-wave anechoic rooms have been used to simulate the electromagnetic wave radiation and the wave reflection properties. A variety of wave absorbers have been proposed for such a wave anechoic room. Most of such wave absorbers are composed of inorganic materials (e.g. Unexamined Patent Publication (Kokai) No. 5-243781) and thereby have a problem of brittleness, while holding sufficient hardness for the purpose of shape-keeping. A pointed part of a pyramidal shape is formed inside the wave anechoic rooms. The brittleness of the material causes the pointed part to be easily broken when being in contact with another object. The inorganic material also makes the wave absorbers undesirably heavy and expensive and does not attain the sufficient nonflammability.
One recently proposed wave absorbing material disclosed in Unexamined Patent Publication (Kokai) No. 8-67544 includes cement, light-weight aggregate, non-conductive fibers, and a synthetic resin emulsion as main constituents and may further have organic microballoons, carbon graphite, or carbon fibers as additional constituents according to the requirements. This prior art technique reduces the weight of the wave absorbing material by using the light-weight aggregate, the synthetic resin emulsion, and the organic microballoons. According to the disclosure of the Publication, however, the possible weight reduction level expressed by the specific gravity is hardly expected to be not less than 0.3. This prior art technique uses cement as the matrix material. It generally requires half a year to a year for exertion of the final strength of cement. The resulting wave absorbing material may accordingly have cracks, due to the volumetric shrinkage in the course of hardening the cement. Namely the prior art technique does not provide the wave absorbing material of the stable properties.
It is required to provide molds suitable for the respective desired shapes. This results in the high manufacturing cost of the wave absorber.
In order to solve the problems arising in the prior art wave absorbers, as results of intensive studies, the present invention provides a wave absorbing material holding both nonflammability and flexibility and having advantageous properties regarding the lightness in weight, the thermal insulation, the sound insulation, the sound isolation, and the workability to ensure a certain freedom in shaping.
The present invention provides a nonflammable wave absorbing material including a conductive filler, an inorganic endothermic filler, and an organic binder as main constituents, wherein all the constituents are integrally layered, and at least one selected from polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer and ethylene-vinyl chloride copolymer is used as the organic binder.
The integrally layered nonflammable wave absorbing material in accordance with claim 17 holds both the inflammability given by the inorganic endothermic filler and the flexibility given by the organic binder.
A preferable example of the conductive filler is carbon black as disclosed in claim 2. The wave absorbing material foamed as disclosed in claim 3 favorably facilitates the integral stratification. In this case, it is preferable that the wave absorbing material further comprises zinc oxide, zinc carbonate, zinc stearate, tribasic lead sulfate, dibasic lead phosphonate, or lead stearate, that reacts with the organic binder to attain the foaming uniformity and the foaming stability (claim 14).
As disclosed in claim 15, the organic binder preferably has a content of 5 to 25% by weight. It is further preferable that the content of the organic binder is 5 to 15% by weight as disclosed in claim 16.
As disclosed in claim 1, the wave absorbing material of a non-integral layered structure may include: (a) a layer of wave absorbing property including a conductive filler and an organic binder (at least one selected from polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer and ethylene-vinyl chloride copolymer) as main constituents; and (b) a layer of endothermic property including an inorganic endothermic filler and an organic binder (at least one selected from polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer and ethylene-vinyl chloride copolymer) as main constituents, wherein the layers (a) and (b) are joined together. Alternatively, as disclosed in claim 17, the wave absorbing material of the non-integral layered structure may have (b) a layer of endothermic property including an inorganic endothermic filler and an organic binder as main constituents, wherein the layer (b) is laid upon one face of a wave absorbing material in accordance with claims 1. In the wave absorbing materials of such structures, the separately prepared layers are joined together to an integral form by means of binding such as adhesion or thermal fusion. This facilitates the manufacture and, in the case where the conductive filler is carbon black, enables the black color of carbon black to be covered with the layer on the endothermic filler side.
In this case the layer (a) of wave absorbing property and/or the layer (b) of endothermic property preferably contain 5 to 25% by weight of the organic binder (claims 1, 15), and more preferably contain 5 to 15% by weight of the organic binder (claims 12, 16).
As disclosed in claims 13 and 3, respectively, the layer (a) of wave absorbing property and/or the layer (b) of endothermic property may be foamed to form the wave absorbing material. Particularly where the layer (b) of endothermic property including the inorganic endothermic filler and the organic binder as the main constituents is foamed, this favorably facilitates the stratification of the endothermic layer. In these cases, the wave absorbing material preferably contains zinc oxide, zinc carbonate, zinc stearate, tribasic lead sulfate, dibasic lead phosphonate, or lead stearate, that reacts with the organic binder to attain the foaming uniformity and the foaming stability (claims 4, 14).
The wave absorbing material in accordance with any one of claims 1-4 and 11-17 may be formed as a whole to a board as disclosed in claim 5 or to a three-dimensional shape as disclosed in claim 6. As disclosed in claim 7, the present invention is also directed to a wave absorber including a wave absorbing material in accordance with any one of claims 2-6 and 11-17. As disclosed in claim 8, the present invention is further directed to a wave anechoic room or a semi-wave anechoic room, in which a wave absorber in accordance with claim 7 is applied for at least part of ceiling, floor, or wall.
The wave absorber may be formed to a pyramidal solid that is suitable for the wave anechoic room or the semi-wave anechoic room.
Any layer included in the wave absorbing material may be formed by foaming and may have a porous network structure for enhanced strength.
The wave absorbing material of the present invention in accordance with any one of claims 1-6 and 11-17 has a variety of applications. In addition to the application for the wave absorber of the wave anechoic room or the semi-wave anechoic room as disclosed in claim 8, the wave absorbing material may be applied for a surface material of a construction, so as to actualize a method of suppressing electromagnetic wave radiation caused by the construction as disclosed in claim 9. The wave absorbing material may also be applied for a wrapping material of an electronic appliance, so as to actualize a method of preventing a leak of electromagnetic wave as disclosed in claim 10.
The present invention is also directed to a method of manufacturing a nonflammable wave absorbing material. The method first mixes calcium carbonate, talc, zinc oxide, a hydroxide, such as aluminum hydroxide or magnesium hydroxide, a foaming agent, and a solvent with a vinyl chloride resin and kneads the mixture. The method adds with stirring, first a conductive filler, such as carbon black, and then a solvent to the kneaded mixture to provide a paste. The method subsequently charges the paste into a mold and applies a pressure and heat to the paste, so as to make the foaming agent foamed and the vinyl chloride resin gelled to react with zinc oxide. The method then cools the mold down and removes a molded object from the mold. The method heats the molded object at ordinary pressure to be foamed and expanded at a predetermined foaming rate. The method finally removes the plasticizer, so as to provide the nonflammable wave absorbing material. This method enables the wave absorbing material to be molded to a desired shape under application of a pressure with a mold. The foamed gas is homogeneously dispersed in the gelled vinyl chloride resin and the inorganic filler. In the meanwhile, the vinyl chloride resin reacts with zinc oxide to enhance the viscosity and the strength of the coat, thereby enabling the formation of a foam with a small quantity of the vinyl chloride resin to facilitate molding of the whole wave absorbing material.
As described above, the wave absorbing material of the present invention has the enhanced nonflammability and improved flexibility to sufficiently avoid possible damages due to the brittleness, while keeping the wave absorbing ability at a comparable level to that of the prior art wave absorbing material. The wave absorber of the present invention formed in a pointed pyramidal shape has sufficient flexibility against the brittleness. The wave absorbing material of the present invention further has favorable workability to attain a certain degree of freedom in shaping and lightness in weight for easy handling, and suitably exerts the thermal insulation, sound isolation, and sound insulation properties. The wave absorbing material of the present invention has a reasonable cost and is favorably applicable for the construction materials having wave absorbing properties and wrapping materials of electronic equipment.
The method of the present invention molds the mixture of the main constituents to manufacture the wave absorbing material having the excellent nonflammability and flexibility. This method is very simple and suitable of mass production and provides the wave absorbing material stably and inexpensively.